Rheostat



March 29, 1960 w. e. MUSHRUSH RHEOSTAT 2 Sheets-Sheet 1 Filed Jan. 22, 1958 Fig.3

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RHEOSTAT Filed Jan. 22, 1958 2 Sheets-Sheet 2 I N V EN TOR. W/Lsou GEOEGEMUSHEUSH H15 A rraeuar United StatesPatent O RHEOSTAT Wilson George Mushrush, Homer City, Pa., assignor to Syntron Company, Homer City, Pa., a corporation of Delaware Application January 22, 1958, Serial No. 710,515

Claims. (Cl. 338-162) This invention relates generally to rheostats and more particularly to improvements in their resistance wire windings and the manner of mounting the same.

Wire wound rheostats which are intended only for providing resistance in circuits have been made from continuous circular windings which also add some inductance to the circuit. This is a particular disadvantage to some circuits.

It is the present practice to wind rheostats in a helical coil around a ceramic bridge member that is subsequently embedded into a slot in a ceramic base member which also supports the slider and knob that engages the wire winding. That portion of the helical coil between the ceramic bridge and ceramic base is completely embedded. This creates an additional problem because that portion of each turn of the helical coil must rely on their adjacent coil turn portions to radiate the heat generated in the wire due to the current resistance that it provides. The embedding of a portion of the coil in this manner creates temperature problems. The ceramic base becomes hotter and it must have a mounting to aid in cooling the same. The actual resistance valves change throughout the coil, making the settings erratic. Thus the temperature and the radiating problems can provide considerable difliculty in the use and mounting of a helical coil wire rheostat. Such difficulties are avoided by the novel structure of this invention.

The principal object of this invention is the provision of a wire wound rheostat that is not in helical coil form but is continuously sinuous and will not produce the inductance produced by a helical coil.

Another object is the provision of bending and shaping the continuous sinuous coil to adapt it to a bridge support so that it may radiate its heat without entrapping it between vtwo mounting members.

Another object is the provision of a wire wound rheostat having a unitary base and bridge that may be made as a single unit initially and the sinuated wire winding applied thereto with the whole of its length exposed for radiating heat.

Other objects and advantages appear hereinafter in the following description and claims.

The accompanying drawings show for the purpose of exemplification without limiting the invention or claims thereto, certain practical embodiments illustrating the principles of this invention wherein:

Fig. 1 is a perspective view of a circular rheostat comprising this invention.

Fig. 2 is a view in section of the rheostat comprising this invention.

Fig. 3 is a perspective view of a longitudinally extending rheostat comprising this invention.

Referring to Figs. 1 and 2 of the drawings, the base 1 is an insulating structure of a ceramic preferably made integral. The base 1 has a mounting flange 2 that forms the perimeter of the base and also functions as a stop or projection beyond the annular bridge or wall portion 3. The outer and inner surfaces 4 and 5 are provided with a 2,931,001 Patented Mar. 29, 1960 An outwardly extending frusto conical boss or slider support 8 is formed integral with the flanged base and has a central bore 10 to receive the bushing 11 having a flange 12 at one end and secured by a nut 13 at its other end. The shaft 14 that extends through the bushing 11 has a knob 15 on one end and is secured to the insulator bushing 16 at its other end. The insulator has opposed recesses 17 to receive the diagonal ears 18 on the washer 20 which also has an interlock, preventing it from turning relative to the shaft 14, and is secured thereto by the screw 21.

The insulator 16 extends through the central opening of the arm 22 which has diagonally disposed slots 23 to receive the abutments 24 on the bushing. Thus theinsulator bushing is locked against relative rotation between the shaft 14 and the arm 22 and any rotary movement of the knob 15 will rotate the arm 22. The arm 22 is metal and rests on the ring 25 which in turn rides on the spring hub section 26 of the terminal 27. The spring hub section 26 maintains contact between itself, the ring 25 and the arm 22 and forms the terminal of this arm or slider, making it a terminal connected slider.

The outer end of the arm or slider 22 has the wire sliding contact member 28 which may be a carbon brush member set into a pocket in the underside of the arm and is connected by the flexible wire 30 to the arm 22 to insure good electrical connection. The arm 22 is set with a permanent bow downwardly to apply contact pressure to the brush member 28, forcing it in electrical contact with a section of the sinuated wire ribbon 31 on the bridge 3.

The sinuated wire ribbon 31 is made up of a continuous series of sinuous parallel passes with their bends along the edges of the ribbons. This flat ribbon is bent longitudinally providing spaced corners that permit it to be formed to the three surfaces 4, 5 and 6 of the bridge 3. The sinuous wire ribbon has uniformly spaced sinu ous passes that maintain their spacing. This formed wire ribbon 31 is then painted on the bridge by an anchoring element that has substantially the hardness as the ceramic and practically all of its attributes. It will not disintegrate due to heat and since it is painted over the. wire each wire pass protrudes as a projection under the paint providing good heat radiating qualities.

The top face of the wire and bridge may have the anchoring cement element cleaned therefrom to expose each lateral pass of the sinuated wire winding to the silder contact 28, but this anchoring cement maintains the spacing between at least two or three adjacent lateral passes. The anchoring cement has an aflinity for the ceramic and penetrates therein so that it must be ground olf if it is desirable to remove some.

Each end of the sinuous wire ribbon 31 has a terminal as indicated at 32 and 33. These terminals are attached by screws 34 passing through the bridge and securing the Wire end as well as the terminal thereto. Thus the winding in the form of the sinuated wire ribbon is terminal connected. The two connections permit this rheostat to be used as a potentiometer as Well as a mere variable resistance.

In the structure of Fig. 3 the long base may be made of suitable insulating material such as a synthetic resin or ceramic. This base has the bridge member 36 and the ends 37 and 38 formed integral with each other. The ends support the rod 40 which is preferably nonround and has terminals 41 at each end thereof. The

slide 42 has a spring biased metal shoe 43 engaging the 7 rod 40 to insure electrical contact therewith. The outer end of the slide carries in a pocket a spring biased button 44 preferably made of suitable electric brush material to have sliding contact with'the wire Winding 45. The brush 44 has soldered thereto a wire that connects directly with the metal shoe 43 so that the slide 42 may be of insulating material. Thus the slider is terminal connected.

The wire winding 45 is mounted on the bridge 36 by a suitable cement that will not disintegrate when subjected to the heat created by the electric current. This wire winding is made from a sinuous ribbon in the same manner as that previously described. The sinuous ribbon has one or more longitudinal bends to shape the ribbon to fit the bridge. If it is desired to extend the ribbon on two faces of the bridge then one bend is sufficient. If it is desired to distribute the ribbon 'on three faces of the bridge then two longitudinal bends are necessary to make the ribbon fit the corresponding faces on the bridge. If the bridge were arcuate or round in cross section the longitudinal bend would be accordingly. When the sinuous wire winding is shaped to fit the bridge and is placed thereon the series of adjacent passes are uniformly spaced but the surfaces of the bridge members may be molded or cut with grooves of the shape of the wire grid making up the sinuous wire ribbon. Such a series of parallel grooves leaves the outer surface of the wire exposed and less anchoring material is necessary to cement the wire winding in place.

If the bridges 3 or 36 are undercut, that is, their transverse dimension is less than the top dimension, the sinuous wire winding which is formed to fit the same hugs or clings to the bridge and if the wire is heavy enough it need not be provided with an anchoring material. The same is true of a structure having a bridge of arcuate or circular cross section. If the ribbon is made of light wire then it is best to anchor the same with a cement or bonding agent even though the bridge is undercut.

I claim:

1. A rheostat having a terminal connected winding of resistance wire carried along a bridge of an insulating base and a terminal connected slider adjustably engaging said resistance wire Winding to vary the resistance between said terminal connections, characterized in that said resistance wire winding is constructed from a flat continuous sinuous ribbon with the wire progressively laid back and forth in consecutive turns each following a wave form, said sinuous ribbon bent longitudinally of its axis to dispose one portion of said ribbon along one face of said bridge and another portion along another face of said bridge, and an anchoring material imper-' vious to the temperature developed in said resistance 4 wire and securing said ribbon to the faces of said insulating bridge, and a bared section along one face of said sinuous ribbon consecutively engaged by said terminal connected slider twice in each turn of a wave form.

2. A rheostat having a terminal connected winding of resistance wire carried along a bridge of an insulating base and a terminal connected slider adjustably engaging said resistance Wire winding to vary the resistance between said terminal connections, characterized in that said resistance Wire winding is a continuous sinuous ribbon bent longitudinally of its axis to dispose one portion of said ribbon along one face of said bridge and another portion along another face of said bridge, and an anchoring material impervious to the temperature developed in said resistance wire and securing said ribbon to the faces of siad insulating bridge, and a bared section along one face of said sinuous ribbon engaged by said terminal connected slider, said sinuous ribbon is bent U-shape in cross section and its opposite sides lie on opposite sides of said bridge.

3. A rheostat'having a terminal connected winding of resistance wire carried along a bridge of an insulating base and a terminal connected slider adjustably engaging said resistance wire winding to vary the resistance between said terminal connections, characterized in that said resistance wire is constructed from a flat, continuous, sinuous ribbon with the wire progressively laid back and forth in consecutive turns each following a wave form and through which the current is to progressively travel through consecutive waves in series along said ribbon, said ribbon extended longitudinally along a face of said bridge and conforming therewith, an anchoring material impervious to the temperature developed in said resistance wire and securing said ribbon to the face of said insulating bridge, the whole and continuous outer face for the full extent of said sinuous ribbon being exposed extenorly from the anchoring material on said insulating bridge, and a bared section along one portion of the face of said sinuous ribbon along said insulating bridge having each of said consecutive turns engaged by the terminal connected slider twice in each consecutive turn of the wire.

4. The structure of claim 3 characterized in that said bridge is straight. i

5. The structure of claim 3 characterized in that said bridge is circular.

References Cited in the file of this patent UNITED STATES PATENTS 528,894 Shaw Nov. 6, 1894 600,057 Ball Mar. 1, 1898 749,204 Kuch Jan. 12, 1904 1,480,953 Ream Jan. 15, 1924 

